1. Technical Field
The invention is concerned with a fabrication of devices best exemplified by Large Scale Integrated circuits built to submicron design rules, e.g. equal to or less than 0.5 .mu.m. Relevant fabrication entails projection lithography using charged particle delineating energy--either electron or ion.
2. Terminology
It is useful to consider specific usage of certain terms in the context of the disclosure.
Optical Field--defines the field area--depending upon context, either for mask or wafer--corresponding with extreme values of angle of incidence of delineating rays (generally for delineating electron rays). It sometimes refers to maximum field permitting needed edge-to-edge resolution. It more generally refers to the actual area resulting from electronic beam scanning,--in one system, to the area electronically scanned before mechanical repositioning of mask or wafer to initiate the next electronic scanning step.
Scanning--as unmodified, refers to movement of the delineating particle beam under the influence of an applied field of varying magnitude. It does not refer to mechanical movement, e.g. of wafer or mask stage, which may be described as "mechanical scanning", "mechanical movement", etc. deBroglie Wavelength--has relavent implications described of the related property for electromagnetic radiation. It is defined as follows: EQU .lambda.=h/p
in which:
.lambda.=deBroglie Wavelength PA1 h=Planck's constant=6.6.times.10.sup.-27 erg-sec PA1 p=momentum=mass.times.velocity
Note: Description is generally in terms of electrons as operating in vacuum. Accordingly, accelerating field energy (e.g. .apprxeq.50-200 kV) is imparted to result in similarly energized electrons (e.g. to result in 50-200 key electrons). While there is some increase in effective mass of the electrons due to relativistic influence, this is largely ignored for purpose of this description.
Transfer of the same energy to ions results in smaller deBroglie wavelength. Since wavelength varies inversely as the square root of particle mass, increasing mass, e.g. by 1800.times.--the mass relationship for a proton relative to an electron--results in a .lambda. value which is approximately 1/42.5 of that of an electron at the same kinetic energy.
Back Focal Plane Filter--The position of this filter is at a cross-over. For the exemplary case of parallel or near-parallel illumination, the cross-over is on the back focal plane or on some equivalent conjugate plane of the lens system.